Investigators from the Ontario Fire Marshall's office prepare to re-enter the home on Laird Dr. where 3 people died in a house fire - Barry Gray,The Hamilton Spectator

A fire that killed three members of a family on the east Mountain in June was caused by careless smoking, an Ontario Fire Marshal investigation has concluded.

Halla Elamein and two of her children in their 20s, Sammy and Sarah Khalil, were overcome by smoke from the fire that began in the basement of their 36 Laird Dr. home June 15.

It was a chilling scene, with firefighters discovering one person behind the front door and another under the living room coffee table. All three were pulled outside where CPR was performed on the front lawn, but it was too late. One was pronounced dead at the scene, two others in hospital.

More than three months later, OFM investigator Richard Derstroff said the investigation is complete.

"The fire was caused by careless smoking," he said.

It's not exactly clear how long it took the fire to begin or what material caught fire first, but an upholstered chair, clothing and other material were all in the basement corner where the fire began.

Fires caused by discarded cigarettes are tricky to measure because they can smoulder for a "significant length of time" before the fire begins, Derstroff said. The smoke from long-smouldering material is especially toxic and can incapacitate people quicker than smoke from a quicker-burning blaze.

There is evidence someone in the home may have tried to initially put the fire out before trying to flee — water was running in the basement laundry sink, he said.

The family had moved from Dundas into the Laid Drive home less than a year before the deadly blaze. They lived in St. Catharines before that.

The children's father died previously and another son, in his early 20s, was away for school at the time of the fire.

Following the fire, friend Deb Goodman described Elamein as a wonderful mother and "the kindest, most compassionate person."

There was a flood of condolence messages online following the fire, including a GoFundMe account set up to benefit the brother left behind. It climbed to more than $10,000 in donations.

There were two smoke alarms in the CityHousing Hamilton home that had been inspected just two weeks before, and were functional.

Derstroff said the smoke alarm in the basement was hard-wired, but did not have backup batteries. It was too damaged from the fire to be tested.

A second smoke alarm upstairs was also hard-wired and when tested appeared to be working. However, nobody appears to have heard the alarm sounding when firefighters arrived shortly before 12:30 a.m. that night.

It's unclear if the smoke was significant enough to cause the upper level alarm to sound.

Neighbours described the family as quiet and nice. The daughter had health issues.

Derstroff cautioned everyone to make sure to have working smoke alarms, and to have an escape plan.

"There should be no reason why anyone should die in a house fire," he said. "Just get out and stay out."